Mass failure to start systemd units on 257.3-1 (with 3rd party glibc)

Description:

After upgrading to systemd 257.3-1 and rebooting, all systemd-related services fail to start.

Additional info:

• systemd + systemd-libs + systemd-sysvcompat versions 257.3-1
• Journal logging stops when the upgrade takes place
  • I've managed to get a dmesg dump after upgrading and not rebooting: dump.txt
• Related BBS posts:
  • https://bbs.archlinux.org/viewtopic.php?id=303424 (main thread)
  • https://bbs.archlinux.org/viewtopic.php?id=303429

Steps to reproduce:

1. Have a working system based on systemd 257.2-2
2. Upgrade at least the following systemd packages to 257.3-1:

• systemd
• systemd-libs
• systemd-sysvcompat

3. Restart/poweroff+on the machine

Expected result:

The machine boots into the normal user session.

Actual behaviour:

After rebooting, almost all service starts (including device mounting & networking) fail. The machine is dropped into a nonfunctional rescue prompt. Rebooting the kernel into rescue or emergency mode also leads to nonfunctional prompts.

I did notice after the systemd upgrade that a subsequent pacman command (pacman -R glibc-eac-bin) was hanging, so I terminated it and rebooted into the broken machine state.